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Fuel Injection System: How Does It Know?

A Fouled Engine Air Filter Can Damage The Mass Air Flow Sensor

With the days of carburetors behind us, the electronic fuel injection system in the cars we drive today is king. While carburetors mixed the air and fuel together and the mixture was sucked into the cylinder and burned, modern electronically controlled fuel injection injects the right amount of fuel, at the right time for optimum fuel efficiency and economy, and driving performance. But the question remains, how does it know what that ‘right amount’ is and when’s the ‘right time’ to inject?

The answer lies in the many sensors located in and around the engine and in the engine’s computer that controls the entire process. The mass air flow (MAF) sensor is at the heart of this system. It includes a piece of very fine wire with an electronic device that measures the amount of air being sucked into the engine and relays that information to the electronic control unit (ECU). Based on this and other information, the ECU decides how much fuel should be injected and when.

“ECUs in modern vehicles are configured to dictate precisely when and how much fuel to inject into the engine for the vehicle to operate at its highest level of efficiency and deliver the best performance of which it is it is capable,” said Kevin O'Dowd, Director of Marketing & Communications for MANN+HUMMEL Purolator Filters, which supplies high quality automotive filters to the North American aftermarket.

With all the air drawn into the engine passing around the MAF sensor, it must consistently act very quickly and accurately just like all the other sensors in a vehicle’s engine management system. In this scenario, if the vehicle’s engine air filter is torn or otherwise compromised and is not replaced, the MAF sensor is unable to assess the amount of air coming in and, as a result, unable to help the ECU determine how much fuel is needed and when.

Furthermore, because the MAF sensor is hot in normal operating conditions, the dirt that hits it sticks and melts, compromising the sensor’s ‘sensing’ capacity.

The engine air filter, therefore, shoulders a big responsibility. It protects the engine from the dirt and dust that blows around us as we drive, and also supports the MAF sensor in its two important tasks of determining – precisely – the quantity of fuel and timing of injection needed for optimum power, economy, and clean emissions.

“We’ve all heard that an ounce of prevention is worth a pound of cure. Nowhere is it more applicable than in the case of a car’s engine air filter. A relatively inexpensive item, simple to find and replace, a car’s engine air filter is more important in the bigger scheme of the ‘environment’ inside a car’s engine,” O'Dowd said.

Purolator offers two types of engine air filters for passenger cars and light trucks -- PureONE and Purolator Classic engine air filters. According to O'Dowd, Purolator’s PureONE engine air filter’s oil-wetted, high-capacity media offers twice the capacity of conventional air filters to trap contaminants smaller than the size of a grain of sand and is 99.5 percent efficient. This means it traps 99.5 percent of particles that size or larger. Likewise, Purolator Classic air filter’s multi-fiber, high-density media traps 96.5 percent of contaminants.

Simply replacing an air filter would cost you approximately $25. On the other hand, with an MAF sensor, which has to be professionally diagnosed and replaced, the cost could jump closer to $400, including parts and labor. While there are chemicals that are commercially available to clean a MAF sensor, the likelihood of success is not high.